Ground vibration transmitted by a surface on which a scale is supported can adversely affect the accuracy of the scale's reading. Scales which use force-sensing transducers, as opposed to mass sensors, are especially prone to this problem. The most common types, including strain gage load cells, are force sensors. It is customary to use low pass filtering techniques to minimize the effects of higher frequency vibrations. However, the effects of vibrations in the frequency range of about 10 Hz or less cannot be satisfactorily attenuated by low pass filtering without greatly increasing the response time of the scale. The increase in response time is unacceptable in many applications, such as postal/shipping scales, in which high throughput is desired.
It is also known to use digital averaging to mitigate the effects of ground vibration but again response time constraints limit the effectiveness of this technique.
It has been proposed to provide, in addition to an article weighing mechanism, a second, or reference, weighing channel. For example, in U.S. Pat. No. 4,751,973, entitled "Load Cell Scale with Reference Channel for Live Load Correction," issued to Freeman et al. and assigned to the assignee of this application, a reference load cell and the primary weighing load cell are mounted in proximity to each other so as to be similarly affected by external vibrations. The output of the reference load cell is averaged over time and a correction term is obtained by dividing that average by the instantaneous output of the reference load cell. The correction term is then applied to the instantaneous output of the weighing channel to compensate for the instantaneous effect of ground vibration. The disclosure of U.S. Pat. No. 4,751,973 is incorporated herein by reference.
Other, more complex approaches to vibration compensation, also using reference channels, are described in references summarized in U.S. Pat. No. 4,751,973. Among these are U.S. Pat. No. 4,624,331 issued to Naito.
While many of these approaches have value, it is desirable to find additional approaches to achieve certain desired cost, response time and accuracy objectives.